JP6177369B2 - Method for producing metal particle aggregate - Google Patents

Description

  The present invention relates to a method for producing a metal-based particle assembly in which a plurality of metal-based particles are two-dimensionally arranged apart from each other.

  It has been known that when metal particles are miniaturized to nano-size, functions that were not seen in the bulk state will be developed. Among them, the application is expected to be “localized plasmon resonance”. is there. Plasmon is a free-electron rough wave generated by collective oscillation of free electrons in a metal nanostructure.

  In recent years, the above-mentioned technical field dealing with plasmons is called “plasmonics” and has attracted a great deal of attention and has been actively researched. Such research has been conducted on light-emitting elements using localized plasmon resonance phenomenon of metal nanoparticles. Including those intended to improve luminous efficiency and conversion efficiency of photoelectric conversion elements (solar cell elements, etc.).

  For example, Patent Documents 1 to 3 disclose techniques for enhancing fluorescence using a localized plasmon resonance phenomenon. Non-Patent Document 1 shows a study on localized plasmon resonance by silver nanoparticles.

JP 2007-139540 A JP 08-271431 A International Publication No. 2005/033335

T. Fukuura and M. Kawashaki, "Long Range Enhancement of Molecular Fluorescence by Closely Packed Submicro-scale Ag Islands", e-Journal of Surface Science and Nanotechnology, 2009, 7, 653

  Patent Document 1 discloses a method of depositing tabular silver particles by performing DC sputtering at a predetermined film deposition rate as a method of forming a large number of tabular metal particles (fluorescence enhancement elements) independent from each other on a substrate. Disclose. The said patent document 2 discloses that a metal island (metal particle) can be formed on a base material by vapor deposition.

  Patent Document 3 discloses the use of an electronic lithography technique as a method for forming a plurality of metal pads (cylindrical protrusions) that cause plasmon resonance on a substrate. In Non-Patent Document 1, as a method of forming a particle aggregate composed of a large number of independent silver particles on a substrate, a sputtering method or a heat treatment (annealing) is performed after spin coating a silver particle dispersion. A method is disclosed.

  However, it is difficult for any of the methods disclosed in the above prior art to control a metal-based particle aggregate having a desired shape (the shape of the metal-based particles and the distance between the particles) according to the purpose of use with good control. There was or was not possible.

  This invention is made | formed in view of the said subject, The objective is to provide the method which can manufacture the metal-type particle aggregate which has a shape suitable for the intended purpose with sufficient control.

The present invention includes the following.
[1] A metal film forming step of forming a metal film having an average thickness of 50 nm or less on a substrate;
A metal-based particle assembly forming step of changing the shape of the metal-based film into a metal-based particle assembly in which a plurality of metal-based particles are two-dimensionally arranged apart from each other by heat treatment;
The manufacturing method of the metal-type particle aggregate containing this.

  [2] The method for producing a metal-based particle assembly according to [1], wherein the temperature of the heat treatment is 280 ° C. or higher.

  [3] The metal according to [1] or [2], wherein the metal-based film forming step includes a step of applying a coating liquid containing particles made of a metal-based material constituting the metal-based film on the substrate. A method for producing a particle assembly.

  [4] The method for producing a metal-based particle assembly according to [3], wherein the concentration of the particles in the coating solution is 0.1 to 7% by weight.

  [5] The method for producing a metal-based particle assembly according to [1] or [2], wherein the metal-based film forming step includes a step of forming the metal-based film on the substrate by a vapor deposition method.

  [6] The metal system according to any one of [1] to [5], wherein a series of steps including the metal film formation step and the metal particle aggregate formation step subsequent thereto are repeated twice or more. A method for producing a particle assembly.

[7] The metal-based particle aggregate includes 30 or more metal-based particles,
The metal-based particles have an average particle diameter in the range of 200 to 1600 nm, an average height in the range of 55 to 500 nm, and an aspect ratio defined by a ratio of the average particle diameter to the average height of 1 to 8 And an average distance between adjacent metal particles (hereinafter also referred to as “average interparticle distance”) is in the range of 1 to 150 nm [1] to [6] The method for producing a metal-based particle assembly according to any one of [6].

[8] The metal-based particle aggregate includes 30 or more metal-based particles,
The metal-based particles have an average particle diameter in the range of 200 to 1600 nm, an average height in the range of 55 to 500 nm, and an aspect ratio defined by a ratio of the average particle diameter to the average height of 1 to 8 In the range of
In the absorption spectrum in the visible light region, the metal-based particle aggregate is a metal particle composed of the same particle size, the same height as the average height, and the same material as the average particle diameter. Compared to the reference metal-based particle aggregate (X) arranged to be in the range of 1 to 2 μm, the maximum wavelength of the peak on the longest wavelength side is shifted to the short wavelength side in the range of 30 to 500 nm. [1] A method for producing a metal-based particle assembly according to any one of [6].

[9] The metal-based particle aggregate includes 30 or more metal-based particles,
The metal-based particles have an average particle diameter in the range of 200 to 1600 nm, an average height in the range of 55 to 500 nm, and an aspect ratio defined by a ratio of the average particle diameter to the average height of 1 to 8 In the range of
In the absorption spectrum in the visible light region, the metal-based particle aggregate is a metal particle composed of the same particle size, the same height as the average height, and the same material as the average particle diameter. Compared with the same number of metal particles, the absorbance at the maximum wavelength of the peak on the longest wavelength side is higher than that of the reference metal particle aggregate (Y) arranged to be in the range of 1 to 2 μm [1. ] The manufacturing method of the metal type particle aggregate in any one of [6].

  [10] The method for producing a metal-based particle assembly according to any one of [1] to [9], wherein the metal-based particles are made of a noble metal.

  [11] The method for producing a metal-based particle assembly according to [10], wherein the metal-based particles are made of silver.

  According to the production method of the present invention, a metal-based particle aggregate having a desired shape (the shape of the metal-based particles and the average distance between the particles) according to the purpose of use can be manufactured with good control.

  According to the manufacturing method of the present invention, since the shape controllability of the metal-based particle aggregate is excellent, a light-emitting element [organic EL (electroluminescence) element, inorganic EL element, inorganic LED (light emitting diode) element, quantum dot light emission It is possible to provide an optical element enhancement element that can significantly improve the luminous efficiency of the element and the like and the conversion efficiency of the photoelectric conversion element (solar cell element and the like) as compared to the conventional one.

It is a schematic sectional drawing for demonstrating the metal type film formation process with which the manufacturing method of the metal type particle assembly of this invention and a metal type particle assembly formation process are equipped. 2 is an AFM image of the metal-based particle assembly 1-1 obtained in Example 1. It is a SEM image (10000 time and 50000 times scale) when the metallic particle assembly 1-2 obtained in Example 1 is seen from right above. 2 is an AFM image of the metal-based particle assembly 1-2 obtained in Example 1. 2 is an AFM image of the metal-based particle assembly 1-3 obtained in Example 1. 2 is an absorption spectrum of the metal-based particle aggregate 1-2 obtained in Example 1. It is a schematic flowchart which shows the manufacturing method of a reference metal type particle aggregate. It is a SEM image (20000 times and 50000 times scale) when a reference metal type particle aggregate is seen from right above. It is a figure explaining the absorption-spectrum measuring method using the objective lens (100 times) of a microscope. 3 is an AFM image of a metal-based particle assembly 2 obtained in Example 2. It is a SEM image (10000 time scale) when the metallic particle assembly 4 obtained in Example 4 is viewed from directly above. 6 is an AFM image of the metal-based particle assembly 4 obtained in Example 4. It is an absorption spectrum of the metal type particle aggregates 2-4 obtained in Examples 2-4. FIG. 14A is a schematic diagram showing a measurement system for an emission spectrum of a photoexcited light emitting device, and FIG. 14B is a schematic cross-sectional view showing a photoexcited light emitting device having a metal particle aggregate and an insulating layer. It is a figure which shows the light emission enhancing effect in the light excitation light emitting element of Examples 5-1 to 5-4. 6 is an AFM image of a metal-based particle assembly 6 obtained in Example 6. 6 is an AFM image of a metal-based particle assembly 7 obtained in Example 7. 4 is an absorption spectrum of metal-based particle aggregates 6 and 7 obtained in Examples 6 and 7. 2 is an AFM image of a silver film H1 obtained in Comparative Example 1. 6 is an AFM image of a silver film H2 obtained in Comparative Example 2. 4 is an absorption spectrum of silver films H1 and H2 obtained in Comparative Examples 1 and 2. 6 is an AFM image of the metal-based particle assembly 8 obtained in Example 8. 6 is an AFM image of a silver film H3 obtained in Comparative Example 3. It is an absorption spectrum of the metal type particle aggregate 8 and the silver film H3 obtained in Example 8 and Comparative Example 3.

<Method for producing metal-based particle assembly>
The present invention relates to a method for producing a metal-based particle aggregate. In the present invention, the “metal-based particle aggregate” is an aggregate of a plurality of metal-based particles (particles made of a metal-based material), and the plurality of metal-based particles are two-dimensionally arranged apart from each other. Say what you are. According to the production method of the present invention, unlike a conventional method, a metal-based particle aggregate having a desired shape (the shape of the metal-based particles and the average interparticle distance, etc.) according to the purpose of use can be manufactured with good control. Can do.

  The “shape” of the metal-based particles refers to “average particle diameter”, “average height”, and “aspect ratio” of the metal-based particles constituting the metal-based particle aggregate. The definitions of “average particle diameter”, “average height”, “aspect ratio” and “average interparticle distance” of the metal-based particles will be described later.

The method for producing a metal-based particle assembly of the present invention includes the following steps:
(A) a metal-based film forming step of forming a metal-based film having an average thickness of 50 nm or less on a substrate; and (B) a metal-based particle aggregate that changes the shape of the metal-based film into a metal-based particle aggregate by heat treatment. Forming step. Hereinafter, each step will be described in detail with reference to FIG.

(A) Metal-based film forming step FIG. 1 (a) is a schematic cross-sectional view for explaining this step, and FIGS. 1 (b) and (c) are metal-based particle aggregate forming steps (B) in the next step. It is a schematic sectional drawing for demonstrating. Referring to FIG. 1A, this step is a step of forming on the substrate 100 a metal film 250 (film made of a metal material) having an average thickness of 50 nm or less. Here, the “average thickness” is a pointed object (tweezers, needle, etc.) provided with a peeling line (scratch) reaching the substrate 100 on the outer surface of the metallic film 250, and the metallic film 250 at this peeling line. An AFM image including the cross section of the substrate 100 and the interface between the metal film 250 and the substrate 100 is acquired, and the distance from the metal film 250 side surface of the substrate 100 to the outer surface of the metal film 250 is randomly selected based on the AFM image. The average value of these 10 points when 10 points are obtained.

  In order to change the shape of the metal-based film 250 into the metal-based particle aggregate substantially completely over the entire region by the metal-based particle aggregate formation step (B) in the next step, the average thickness of the metal-based film 250 is set to 50 nm. It is necessary to: The average thickness of the metal film 250 is preferably 40 nm or less, more preferably 30 nm or less, and still more preferably 20 nm or less. When the average thickness of the metal-based film 250 exceeds 50 nm, depending on the heat treatment temperature or the like in the metal-based particle assembly forming step (B), the shape may be partially changed into the metal-based particle assembly. At least most of the film becomes a continuous film, and it is difficult to convert the metal film 250 into a metal particle aggregate over the entire region. Although depending on the heat treatment temperature in the metal-based particle assembly forming step (B), generally, the larger the average thickness of the metal-based film 250, the larger the average particle diameter and the higher the average metal height. A system particle aggregate is obtained.

  The average thickness of the preferable metal-based film 250 is 40 nm or less, the more preferable average thickness is 30 nm or less, and the more preferable average thickness is 20 nm or less. The metal-based particle aggregate having specific characteristics such as exhibiting extremely strong plasmon resonance as compared with the prior art by having a distance, etc., and suitable as an enhancement element for optical elements including light-emitting elements and photoelectric conversion elements This is because it can be formed with good control.

  The lower limit value of the average thickness of the metal film 250 is not particularly limited, but a predetermined shape (average particle diameter of metal particles 200 to 1600 nm, which the metal particle aggregate suitable as an enhancement element of the optical element as described above has, In order to achieve an average height of 55 to 500 nm, an aspect ratio of 1 to 8, and an average inter-particle distance of 1 to 150 nm. 10 nm or more is more preferable, and 15 nm or more is more preferable. However, when producing a metal-based particle assembly by repeating a series of steps including the metal-based film forming step (A) and the metal-based particle assembly forming step (B) twice or more, the metal system in each round The lower limit value of the average thickness of the film 250 may be smaller than the preferable lower limit value.

  A preferred example of a method of forming the metal film 250 on the substrate 100 is a particle made of the same material as the metal material constituting the metal film 250 (hereinafter, this particle is used to form a metal particle aggregate “metal system”). This is a method of applying a coating solution containing “particles” to distinguish from “particles”. The coating solution is typically a dispersion in which the above particles are dispersed in a solvent. When the coating solution contains a solvent, the coating film is dried before the step (B) as necessary.

  Examples of the application method of the coating liquid include spin coating, bar coating, gravure coating, micro gravure coating, roll coating, rod coating, knife coating, air knife coating, kiss coating, and die coating. Although it may be a conventionally known method, the spin coating method is preferable from the viewpoint of the high uniformity of the film thickness of the metal film 250 obtained. On the other hand, a web coating method such as a gravure coating method is preferable from the viewpoint that roll film formation is possible and productivity is excellent. The coating solution may be applied two or more times as necessary (for example, to achieve a desired average thickness).

  As described above, the coating solution typically contains the particles and the solvent. As the coating solution, a commercially available product can be used, or a solution obtained by adding an additive such as a surfactant or a diluent solvent to the product can be used. Of course, a dispersion prepared by adding the particles and optionally added additives to the solvent may be used as the coating solution. As the solvent, various organic solvents, aqueous solvents such as water, or a mixture thereof can be used. The particles are not particularly limited as long as the particles include the metal-based material constituting the metal-based film 250 and may be modified such as surface treatment, but only from the metal-based material not subjected to any modification. It may be. The method of the present invention is also advantageous in that normal particles without any modification (for example, dispersions of particles that are generally not commercially available without any modification) can be used.

  The average particle diameter of the particles contained in the coating solution is usually 1 to 50 nm, more typically 1 to 40 nm, and preferably 1 to 20 nm. Within the range of 1 to 50 nm, although depending on the concentration of the particles in the coating solution, a metal film 250 having an average thickness of 50 nm or less is easily obtained. Note that even when the average particle diameter of the particles exceeds 50 nm, it is possible to obtain the metal-based film 250 having an average thickness of 50 nm or less. Therefore, particles having an average particle diameter exceeding 50 nm can also be used.

  The concentration of the particles in the coating solution is preferably 0.1 to 7% by weight. When the particle concentration exceeds 7% by weight, when the coating solution is applied by the usual application method exemplified above, the average particle size of the particles and the application method (the type of application method such as spin coating method and bar coating method, and Depending on the number of revolutions in the spin coating method and the coating method such as the line speed in the roll coating method, the average thickness tends to exceed 50 nm even with a single coating. The upper limit of the particle concentration is more preferably 5% by weight. The use of a coating liquid having a particle concentration of 0.1 to 7% by weight also allows the coating liquid to be applied substantially evenly over the entire coating liquid coating area without causing an excessively excessively applied portion or an insufficiently coated portion. preferable. This further ensures that the metal film 250 is converted into a metal particle aggregate over the entire region.

  On the other hand, when the particle concentration is extremely low, the density of the metal-based film 250 is extremely sparse, and the amount of the metal-based material that can be supported on the substrate is reduced by one coating, so that the metal-based particles are densely packed. It is difficult to obtain an arranged metal-based particle aggregate. Accordingly, in order to obtain a metal particle aggregate having specific characteristics such as dense arrangement of metal particles (for example, an average interparticle distance of 1 to 150 nm) and exhibiting extremely strong plasmon resonance as compared with the prior art. The particle concentration is preferably 0.1% by weight or more as described above. However, in the case of applying the coating solution twice or more in the metal-based film forming step (A), or a series of steps including the metal-based film forming step (A) and the metal-based particle aggregate forming step (B) twice or more. By repeating, when manufacturing a metal-type particle aggregate, the particle concentration of the coating liquid at each time may be less than 0.1% by weight.

  The particle concentration of the coating solution is more preferably 0.25% by weight or more, and further preferably 0.8% by weight or more. This is the number of repetitions of application of the coating liquid in one metal-based film formation step (A), and the number of repetitions of a series of steps including the metal-based film formation step (A) and the metal-based particle aggregate formation step (B). Metal particle aggregate in which metal particles are densely arranged, and further, a metal particle aggregate extremely suitable as an enhancement element of an optical element exhibiting a high plasmon resonance effect It is because it can be obtained. Reducing the number of repetitions of application and the number of repetitions of the above-described series of steps is advantageous for the film thickness uniformity of the metal-based film 250.

  On the other hand, when the web coating method is adopted as the coating method, it is easy to form a uniform metal film 250 having an average thickness of 50 nm or less, so the particle concentration of the coating solution should be 0.15 wt% or less. Is more preferable.

  As described above, in the present invention, in order to manufacture a metal-based particle aggregate having a desired shape according to the purpose of use (the shape of the metal-based particles and the average distance between the particles, etc.) with good control, It is important to set the average thickness to a predetermined thickness or less. And as a coating method for achieving this predetermined average thickness, various coating methods as listed above can be adopted in the present invention. The particle concentration of the coating solution is appropriately selected according to the coating method so that a predetermined average thickness can be achieved. In other words, even if a specific particle concentration of the coating liquid is unsuitable for a coating method, metal particles having a desired shape using this coating liquid by adopting another coating method in the present invention. The assembly can be manufactured with good control. The method of the present invention is also advantageous in that a highly productive coating method such as web coating can be employed.

  Another preferred example of the method for forming the metal-based film 250 on the substrate 100 is a vapor deposition method in which vapor of a metal-based material is deposited on the substrate 100. In this case, the metal film 250 having an average thickness of 50 nm or less can be obtained by adjusting the deposition rate, the deposition time, and the like. The preferred average thickness is the same as above.

  As a method for forming the metal film 250 on the substrate 100, a sputtering method, a plating method, or the like can be used.

  When the metal-based material constituting the metal-based particles of the metal-based particle aggregate (metal-based material composing the metal-based film 250) is a nanoparticle or an aggregate thereof, the absorption spectrum measurement using an absorptiometry is performed in the ultraviolet to A material that exhibits a plasmon resonance peak (hereinafter also referred to as a “plasmon peak”) that appears in the visible region is preferable. For example, a noble metal such as gold, silver, copper, platinum, or palladium, or a metal such as aluminum or tantalum; Examples of the noble metal or metal-containing alloy include metal compounds (metal oxides, metal salts, etc.) containing the noble metal or metal, among which noble metals such as gold, silver, copper, platinum, and palladium are preferable. From the viewpoint of low cost and low absorption (small imaginary part of dielectric function at visible light wavelength), silver is more preferable. The type of material is the use of the metal particle aggregate (for example, the type of the optical element when the metal particle aggregate is applied as an enhancement element of the optical element using the plasmon resonance effect), and the enhancement It is preferable to select appropriately according to the absorption spectrum peak wavelength, emission spectrum peak wavelength, reflection spectrum peak wavelength, etc. of the active layer of the optical element.

The material constituting the substrate 100 can be selected from a wide range, and in particular, a substrate on which metal-based particle assemblies are stacked (hereinafter also referred to as “metal-based particle assembly stacked substrate”) has its plasmon resonance effect. When using as a reinforcing element for an optical element, it is preferable to use a substrate made of a non-conductive material. This is because the plasmon resonance effect is reduced when electrons can be transferred between some or all of the metal-based particles via the substrate. Examples of non-conductive materials include glass, various inorganic insulating materials (SiO ₂ , ZrO ₂ , mica, etc.), various plastic materials, and the like. The surface of the substrate 100 on which the metal film 250 is formed is preferably as smooth as possible.

  In addition, when the metal-based particle assembly laminated substrate is applied as, for example, an enhancement element of a light-emitting element, light can be extracted from the substrate surface (surface opposite to the metal-based particle assembly). It is preferable to use a light-transmitting substrate, and it is more preferable to use an optically transparent substrate.

  The outer surface of the metal-based film 250 formed on the substrate 100 by the method described above is not completely flat but has a certain uneven shape (FIG. 1A). reference).

(B) Metal-based particle assembly forming step Referring to FIGS. 1B and 1C, this step is performed by heat-treating (annealing) a metal-based film 250 having an average thickness of 50 nm or less. This is a step of changing the shape to the metallic particle aggregate 200. By this step, as a main form change, the surface region 255 of the metal-based film 250 (this surface region is typically a metal oxide by heat) is thermally decomposed (see FIG. 1B). ), A shape change occurs where the metal film 250 is cut off at the valleys of the surface unevenness of the metal film 250, and the metal particle aggregate 200 composed of a plurality of metal particles 201 arranged independently of each other is formed. (See FIG. 1C). In addition to such major shape changes, 1) shape change in which the surface shape of the metal-based film 250 that has received heat changes before the metal-based film 250 is cut off, and 2) formed metal-based particles. Morphological change in which 201 merges with adjacent metal-based particles 201 and particle growth 3) Morphological change in which the surface region of the formed metal-based particle 201 is thermally decomposed to cause particle reverse growth (particle miniaturization), etc. There are also secondary morphological changes. The shape of the obtained metal-based particle aggregate 200 depends on the heat treatment conditions, more specifically, the contribution of the main shape change and the secondary shape change depending on the heat treatment conditions.

  The temperature of the heat treatment is preferably 280 ° C. or higher, more preferably 285 ° C. or higher. Moreover, the temperature of heat processing is 600 degrees C or less normally, Preferably it is 580 degrees C or less. When the temperature is higher than the temperature at which the surface region 255 of the metal-based film 250 starts to thermally decompose (for example, about 150 to 200 ° C. when the surface region is made of silver oxide), the above-described main form change and secondary form Changes can occur. However, when the heat treatment temperature is less than 280 ° C., the shape change may take a long time, or the shape change may occur only with an extremely thin metal film 250 having an average thickness of less than 30 nm. Therefore, it tends to be difficult to obtain a metal particle aggregate having a desired shape.

  When the temperature of the heat treatment exceeds 600 ° C., the secondary morphological change of the above 3) that occurs after the formation of the metal particles 201 independent from each other becomes remarkable, and the metal particles 201 disappear from the substrate 100. It is easy to end up.

  By adjusting the heat treatment temperature, it is possible to produce a metal particle aggregate having a desired shape according to the purpose of use. For example, when the average thickness of the metal-based film 250 is about 30 nm or less, any of heat treatment in a low temperature region of about 280 to about 500 ° C. and heat treatment in a high temperature region of about 500 to about 600 ° C. It is possible to obtain a metal-based particle aggregate exhibiting a strong plasmon peak (showing a high plasmon resonance effect). At this time, as the heat treatment temperature is higher, a metal particle aggregate composed of metal particles having a larger average particle diameter and average height tends to be obtained. However, in the heat treatment in the high temperature region, if the heat treatment time is excessively long, the secondary shape change of 3) that occurs after the metal-based particles 201 independent from each other are formed becomes conspicuous. In some cases, the metal-based particles 201 may disappear from the substrate 100.

  When the average thickness of the metal film 250 is more than about 30 nm and less than 50 nm, a metal particle aggregate that exhibits a strong plasmon peak (shows a high plasmon resonance effect) by heat treatment in a high temperature region of about 500 to about 600 ° C. It is possible to get a body. Even when the average thickness of the metal-based film 250 is more than about 30 nm and not more than 50 μm, the higher the heat treatment temperature, the more likely the metal-based particle aggregate composed of metal-based particles having a larger average particle diameter and average height is obtained. is there. However, if the heat treatment time is excessively long, the secondary morphological change of the above 3) that occurs after the formation of the metal particles 201 independent from each other becomes significant, and finally the metal particles are formed on the substrate 100. 201 may disappear.

  The heat treatment time is usually several seconds to several hours, preferably 10 seconds to 1 hour, more preferably 30 seconds to 30 minutes. If the heat treatment time is excessively short, the shape change to the metal-based particle aggregate becomes insufficient, and if it is excessively long, the amount of heat treatment exceeding the time required to complete the shape change is wasted, and the process time is wasted. In some cases, the secondary morphological change of 3), which occurs after the metal particles 201 independent of each other are formed, becomes prominent, and the metal particles 201 may disappear from the substrate 100. In addition, when the heat treatment time at a relatively high temperature is excessively long, even if the average thickness of the metal-based film 250 is the same, the secondary shape change of the above 3) becomes remarkable. Since the average interparticle distance of 201 becomes excessively large, the strong plasmon resonance effect obtained by densely arranging the metal-based particles 201 tends to be difficult to obtain, and the metal formed on the substrate 100 When the number of the system particles 201 is smaller than a desirable number (30) described later, a strong plasmon resonance effect tends to be difficult to obtain from this viewpoint.

  The environment during the heat treatment is not particularly limited, and may be any of an oxidizing atmosphere, a reducing atmosphere, a vacuum atmosphere, and an inert gas atmosphere. For example, it can be performed in an air atmosphere. Especially, since the form change by oxidative decomposition (thermal decomposition of a metal oxide) can be performed suitably, an oxidizing atmosphere, especially an air atmosphere is preferable.

  In the present invention, a metal-based particle assembly may be produced by repeating a series of steps including the metal-based film forming step (A) and the subsequent metal-based particle assembly forming step (B) twice or more. preferable. According to such a method, by repeating the main shape change and the secondary shape change of the metal film 250 due to the supply of the metal material for forming the metal film 250 and the subsequent heat treatment, the metal particles The average particle size, average height, aspect ratio, and average interparticle distance of the metal-based particles are in a range that is difficult to carry out only by performing the above series of steps only once. It becomes easier to control. Moreover, by making the heat treatment time in each metal-based particle aggregate formation step (B) relatively short (for example, about 20 to 60 seconds), the metal-based particles can be arranged relatively densely (average interparticle distance). Can be reduced).

  Therefore, the method of repeating the above-described series of steps is a metal particle aggregate that requires control of a more precise shape (the shape of the metal particles and the average distance between the particles), that is, in comparison with the conventional method. It has specific characteristics such as showing extremely strong plasmon resonance, and is suitable for the production of a metal-based particle aggregate described in detail below, which is suitable as an enhancement element for optical elements including light-emitting elements and photoelectric conversion elements.

In addition, when the case where the above series of steps is repeated twice is taken as an example, the first time is the same as the above steps (A) and (B).
(A1) a first metal-based film forming step of forming a first metal-based film having an average thickness of 50 nm or less on the substrate; and (B1) the first metal-based film is formed into a first metal-based film by heat treatment. Including a first metal-based particle assembly forming step of changing the shape into a particle assembly,
(A2) a second metal-based film forming step for forming a second metal-based film on the first metal-based particle aggregate; and (B2) the first metal-based particle aggregate and the first metal film by heat treatment. A second metal-based particle assembly forming step of obtaining a second metal-based particle assembly in which a plurality of second metal-based particles are two-dimensionally arranged apart from each other from the two metal-based films. .

  That is, in the step (B2), the first metal-based particle aggregate obtained in the step (B1) and the second metal-based film formed thereon are integrated by heat treatment to form the second The shape changes to a metallic particle aggregate.

  Regarding the metal film forming conditions in the step (A2) and the heat treatment conditions in the process (B2), the contents described above for the metal film forming process (A) and the metal particle aggregate forming process (B) are cited, respectively. The metal film forming conditions in the steps (A1) and (A2) and the heat treatment conditions in the steps (B1) and (B2) may be the same or different.

  The average thickness of the second metal film formed in the step (A2) is preferably 50 nm or less for the same reason as described above. The average thickness of the second metal-based film here is the same as that when forming on the first metal-based particle aggregate (for example, when applying a coating liquid, the same area, the same composition, The average thickness according to the above definition for the metal film when the metal film is formed on a flat substrate with the same coating method and the same coating amount.

  In the metal-based particle aggregate formed on the substrate 100 obtained as described above, the metal-based particles are insulated from each other, in other words, non-conductive (metal) between adjacent metal-based particles. It is preferable that the system particle aggregate is non-conductive. This is because the plasmon resonance effect is reduced when electrons can be transferred between some or all of the metal-based particles. Therefore, for the same reason, it is preferable that the metal-based particles are reliably separated from each other and no conductive substance is interposed between the metal-based particles.

  In addition, the manufacturing method of this invention may include the process of forming an insulating layer in the surface of a metal type particle aggregate so that it may explain in full detail later.

<Metal-based particle assembly>
As described above, according to the production method of the present invention, it is possible to produce a metal-based particle aggregate having a desired shape (the shape of the metal-based particles and the average distance between the particles) with good control. Therefore, the present invention is useful as a method for producing a metal-based particle aggregate having specific characteristics such as exhibiting extremely strong plasmon resonance that is first manifested by precise shape control. This metal-based particle aggregate, which is a plasmon material, can be suitably applied as an enhancement element for optical elements including light-emitting elements and photoelectric conversion elements, and can improve the luminous efficiency of the applied light-emitting elements and the conversion efficiency of the photoelectric conversion elements. This can be significantly improved as compared with the prior art.

  An example of the above-described metal-based particle aggregate suitable as an optical element enhancement element, which can be obtained by the production method of the present invention, has 30 or more metal-based particles arranged two-dimensionally apart from each other. The average particle diameter of the metal-based particles is in the range of 200 to 1600 nm, the average height is in the range of 55 to 500 nm, and the aspect ratio defined by the ratio of the average particle diameter to the average height is in the range of 1 to 8. And a metal-based particle aggregate having any of the following characteristics.

[I] The metal-based particles constituting the metal-based particle aggregate are arranged so that the average distance (average interparticle distance) between the adjacent metal-based particles is in the range of 1 to 150 nm (hereinafter, This metal-based particle aggregate is also referred to as “metal-based particle aggregate [i]”),
[Ii] The metal-based particle aggregate is a distance between the metal-based particles in the absorption spectrum in the visible light region, wherein the metal-based particles having the same particle size, the same height as the average height, and the same material are used. Compared to the reference metal particle aggregate (X) arranged so that all are in the range of 1 to 2 μm, the peak maximum wavelength on the longest wavelength side shifts to the short wavelength side in the range of 30 to 500 nm. (Hereinafter, this metal-based particle aggregate is also referred to as “metal-based particle aggregate [ii]”).
[Iii] The metal-based particle aggregate has a distance between the metal-based particles that is the same as the average particle diameter, the same height as the average height, and the same material in the absorption spectrum in the visible light region. In comparison with the same number of metal particles, the absorbance at the maximum wavelength of the peak on the longest wavelength side is higher than that of the reference metal particle aggregate (Y) arranged so that all are in the range of 1 to 2 μm (Hereinafter, this metal-based particle aggregate is also referred to as “metal-based particle aggregate [iii]”).

  In contrast to the reference metal-based particle aggregate, the average particle diameter and the average height are “same” as the reference metal-based particle aggregate (X) or (Y). The difference in average particle diameter is ± 45 nm. It means that the difference in average height is within a range of ± 15 nm.

  For example, in emission enhancement using the localized plasmon resonance phenomenon of conventional plasmon materials (metal nanoparticles or aggregates thereof), the range of action of localized plasmon resonance is within a very narrow range of 10 nm or less from the surface of the metal nanoparticles. There was a problem of being limited. This is because as the distance between the metal nanoparticle and the molecule to be excited increases, the localized plasmon resonance no longer effectively affects the light emission enhancement effect, and the energy transfer of the Forster mechanism appears. This is because if the range (1 nm to 10 nm) is exceeded, almost no light emission enhancement effect can be obtained. Also in the light emission enhancement methods described in Patent Documents 1 to 3, the distance between the metal nanoparticles effective for obtaining an effective light emission enhancement effect and the excited molecule is 10 nm or less.

  Therefore, the enhancement effect of the optical element utilizing the local plasmon resonance phenomenon of the conventional metal nanoparticles or aggregates thereof is not always satisfactory because of the limitation of the action range of the local plasmon resonance. That is, when the optical element has an active layer having a thickness of several tens of nanometers or more (for example, a light emitting layer of a light emitting element, a light absorbing layer of a photoelectric conversion element), the metal nanoparticles are temporarily close to the active layer, Or even if it can be placed inside, the direct enhancement effect by localized plasmon resonance can be obtained only in a part of the active layer, so the luminous efficiency and conversion efficiency improvement effect is partial. Met.

  In contrast, the metal particle aggregates [i] to [iii] that can be obtained by the production method of the present invention are considered that the metal particles constituting the metal particle aggregates generally have a small light emission enhancing effect. Despite having a relatively large particle size (see paragraphs 0010 to 0011 of Patent Document 1 above), plasmon that exhibits extremely strong plasmon resonance and is significantly elongated due to having a specific shape, etc. The range of action of resonance (the range covered by the plasmon enhancement effect) is shown.

Hereinafter, the metal particle aggregates [i] to [iii] will be described in detail.
(Metal-based particle aggregate [i])
The metal-based particle aggregate [i] is extremely advantageous in the following points.

  (1) Since it exhibits extremely strong plasmon resonance, when applied to a light-emitting element, a stronger light emission enhancement effect can be obtained compared to the case of using a conventional plasmon material, thereby dramatically improving the light emission efficiency. Can be increased. Moreover, when it applies to a photoelectric conversion element, the conversion efficiency can be improved greatly. The intensity of the plasmon resonance indicated by the metal-based particle aggregate [i] is not a mere sum of the localized plasmon resonances exhibited by individual metal-based particles at a specific wavelength, but is higher than that. That is, when 30 or more metal particles having a predetermined shape are densely arranged at the predetermined interval, individual metal particles interact with each other, and extremely strong plasmon resonance is expressed. This is considered to be expressed by the interaction between the localized plasmons of the metal-based particles.

  In general, when an absorption spectrum of a plasmon material is measured by absorptiometry, a plasmon peak is observed as a peak in the ultraviolet to visible region. The metal-based particle aggregate [i] formed on the glass substrate has a maximum wavelength of the plasmon peak on the longest wavelength side in the visible light region when the absorption spectrum is measured. Can be 0.4 or more, further 0.7 or more, and even 0.9 or more.

The absorption spectrum of the metal-based particle aggregate is measured by absorptiometry using a sample formed on a glass substrate as a measurement sample. Specifically, the absorption spectrum is on the back side of the glass substrate on which the metal-based particle aggregates are laminated (on the side opposite to the metal-based particle aggregates), and is in the ultraviolet to visible light region from the direction perpendicular to the substrate surface. Is a substrate having the same thickness and material as that of the substrate of the measurement sample, and the metal particle aggregate is laminated. By irradiating the same incident light from the direction perpendicular to the surface of the non-substrate and measuring the intensity I ₀ of the transmitted light in all directions transmitted from the opposite side of the incident surface using an integrating sphere spectrophotometer, respectively. can get. At this time, the absorbance, which is the vertical axis of the absorption spectrum, has the following formula:
Absorbance = −log ₁₀ (I / I ₀ )
It is represented by

  (2) The action range of plasmon resonance (the range in which the enhancement effect by plasmons reaches) is significantly extended. Such an elongation action is also considered to be manifested by the interaction between localized plasmons of metal-based particles generated by densely arranging 30 or more predetermined-shaped metal particles at a predetermined interval. According to the metal-based particle aggregate [i], it is possible to extend the plasmon resonance action range, which is conventionally limited to the range of about the Forster distance (about 10 nm or less), to about several hundred nm, for example.

  The extension of the plasmon resonance operating range as described above is extremely advantageous for enhancing optical elements such as light emitting elements and photoelectric conversion elements. That is, due to the significant extension of this working range, even if the active layer has a thickness of several tens of nanometers or more, it becomes possible to enhance the entire active layer, thereby enhancing the optical element. (Emission efficiency, conversion efficiency, etc.) can be significantly improved.

  In the conventional plasmon material, the plasmon material has to be arranged so that the distance from the active layer is within the range of the Förster distance. According to the metal-based particle aggregate [i], the active layer Therefore, for example, the enhancement effect by plasmon resonance can be obtained even if they are arranged at a position 10 nm, further several tens of nm (for example, 20 nm), or even several hundred nm apart. This means that, for example, in the case of a light-emitting element, the metal-based particle aggregate can be disposed in the vicinity of the light extraction surface considerably away from the light-emitting layer. It is possible to suppress the total reflection at the interfaces of the various light emitting element constituting layers that pass through until the light emitted from the light reaches the light extraction surface, so that the light extraction efficiency can be improved.

  As described above, the metal-based particle aggregate [i] uses such a large-sized metal particle in spite of using relatively large-sized metal-based particles that are difficult to generate dipole-type localized plasmons in the visible light region. By arranging a specific number or more of metal-based particles (although it is necessary to have a predetermined shape) closely spaced with a specific interval, an extremely large number of the metal-based particles included in the large-sized metal particles The surface free electrons can be effectively excited as plasmons, and it is possible to realize remarkably strong plasmon resonance and a significant extension of the range of action of plasmon resonance.

  In addition, the metal particle aggregate [i] has a structure in which a specific number or more of relatively large metal particles having a specific shape are two-dimensionally spaced apart at a specific interval. As a result, the following advantageous effects can be obtained.

  (3) In the absorption spectrum in the visible light region, the maximum wavelength of the plasmon peak can show a specific shift depending on the average particle diameter of metal-based particles and the average interparticle distance. Specifically, the maximum wavelength of the plasmon peak on the longest wavelength side in the visible light region shifts to the short wavelength side (blue shift) as the average particle size of the metal-based particles increases with a constant average interparticle distance. To do. Similarly, as the average particle size of large metal particles is kept constant and the distance between the average particles is decreased (when metal particles are arranged more densely), the maximum of the plasmon peak on the longest wavelength side in the visible light region The wavelength shifts to the short wavelength side. This peculiar phenomenon is the Mie scattering theory generally accepted for plasmon materials [in accordance with this theory, the maximum wavelength of the plasmon peak shifts to the longer wavelength side (red shift) as the particle size increases. ] Is against this.

  The unique blue shift as described above also has a structure in which the metal-based particle aggregate [i] has a structure in which large-sized metal particles are densely arranged at specific intervals. This is thought to be due to the interaction between the localized plasmons of. The metal-based particle aggregate [i] (in a state of being laminated on the glass substrate) has the longest absorption spectrum in the visible light region measured by the absorptiometry according to the shape of the metal-based particles and the average interparticle distance. The plasmon peak on the wavelength side can exhibit a maximum wavelength in a wavelength region of 350 to 550 nm, for example. Further, the metal-based particle aggregate [i] typically has a thickness of about 30 to 500 nm (for example 30 to 30 nm) as compared with the case where the metal-based particles are arranged with a sufficiently long inter-particle distance (for example, 1 μm). 250 nm) blue shift can occur.

  Such a metal-based particle aggregate in which the maximum wavelength of the plasmon peak is blue-shifted compared to the conventional one is extremely advantageous, for example, in the following points. That is, while there is a strong demand for a blue (or near-wavelength region, hereinafter the same) luminescent material (especially a blue phosphorescent material) that exhibits high luminous efficiency, development of such a material that can withstand practical use is currently underway. However, it is difficult to use a blue light emitting material with relatively low luminous efficiency by applying, for example, a metallic particle aggregate [i] having a plasmon peak in the blue wavelength region as an enhancement element to a light emitting element. However, the luminous efficiency can be increased to a sufficient level. In addition, when applied to photoelectric conversion elements (solar cell elements, etc.), for example, the wavelength region that could not be used in the active layer itself can be effectively utilized by blue shifting the resonance wavelength, thereby improving the conversion efficiency. obtain.

Next, the specific configuration of the metal-based particle aggregate [i] will be described in more detail.
The average particle size of the metal-based particles is in the range of 200 to 1600 nm, and in order to effectively obtain the effects (1) to (3) above, preferably 200 to 1200 nm, more preferably 250 to 500 nm, still more preferably Is in the range of 300-500 nm. The average particle diameter of the metal-based particles is preferably selected appropriately depending on the type of optical element to which the metal-based particle aggregate is applied as an enhancement element and the type of material constituting the metal-based particles.

  What should be noted here is that, for example, large metal particles having an average particle diameter of 500 nm, as described above, hardly show an enhancement effect by localized plasmons alone. On the other hand, the metal particle aggregate [i] has an extremely strong plasmon resonance and plasmon resonance action by densely arranging a predetermined number (30) or more of such large metal particles at a predetermined interval. The remarkable extension of the range and further the effect (3) are realized.

  The average particle size of the metal-based particles means that 10 particles are randomly selected in the SEM observation image from directly above the metal-based particle assembly in which the metal-based particles are two-dimensionally arranged, and each particle image includes Randomly draw 5 tangential diameters (however, any straight line with a tangential diameter can only pass through the interior of the particle image, one of which is only the interior of the particle and is the longest drawable line) The average value of the 10 selected particle sizes when the average value is the particle size of each particle. The tangent diameter is defined as a perpendicular line connecting the interval (projection image) of a particle between two parallel lines in contact with it (Nikkan Kogyo Shimbun “Particle Measurement Technology”, 1994, page 5). .

  The average height of the metal-based particles is in the range of 55 to 500 nm, and in order to effectively obtain the effects (1) to (3), preferably in the range of 55 to 300 nm, more preferably 70 to 150 nm. It is. The average height of the metal-based particles refers to 10 measured values when 10 particles are randomly selected in the AFM observation image of the metal-based particle aggregate and the heights of these 10 particles are measured. Average value.

  The aspect ratio of the metal-based particles is in the range of 1 to 8, and it is preferable that the metal-based particle aggregate is appropriately selected depending on the type of the optical element to which the metal-based particle aggregate is applied as the enhancement element. For example, when used as an enhancement element of a light emitting device, the metal-based particles tend to have a flat shape. In this case, in order to obtain a higher enhancement effect, the aspect ratio is preferably 2 to 8. 2.5 to 8 is more preferable. On the other hand, when used as an enhancement element of a photoelectric conversion element, in order to obtain a higher enhancement effect, the metal particles tend to be more preferable as they are closer to a true sphere. The aspect ratio of the metal-based particles is defined by the ratio of the average particle diameter to the average height (average particle diameter / average height).

  From the viewpoint of exciting highly effective plasmons, the surface of the metal-based particles is preferably a smooth curved surface, but the surface may contain some minute irregularities (roughness). The metal particles may be indefinite.

  In view of the uniformity of the intensity of plasmon resonance in the plane of the metal-based particle aggregate, it is preferable that the size variation between the metal-based particles is as small as possible. However, even if there is some variation in the particle size, it is not preferable that the distance between the large particles is increased, and it is preferable that the interaction between the large particles is facilitated by filling the space between the small particles.

  In the metal particle aggregate [i], the metal particles are arranged such that the average distance (average interparticle distance) between the adjacent metal particles is in the range of 1 to 150 nm. By arranging the metal-based particles densely in this way, it is possible to achieve extremely strong plasmon resonance, a significant extension of the plasmon resonance action range, and further the effect (3) above. In order to effectively obtain the effects (1) to (3) above, the average interparticle distance is preferably in the range of 1 to 100 nm, more preferably 1 to 50 nm, and even more preferably 1 to 20 nm. When the average interparticle distance is less than 1 nm, electron transfer based on the Dexter mechanism occurs between particles, which is disadvantageous in terms of deactivation of localized plasmons.

  The average interparticle distance means that 30 particles are randomly selected in an SEM observation image from directly above a metal particle aggregate in which metal particles are two-dimensionally arranged, and each selected particle is adjacent to each other. It is the average value of the interparticle distances of these 30 particles when the interparticle distance with the matching particles is obtained. The inter-particle distance between adjacent particles is a value obtained by measuring the distances between all adjacent particles (the distance between the surfaces) and averaging them.

  The number of metal particles contained in the metal particle aggregate [i] is 30 or more, preferably 50 or more. By forming an aggregate containing 30 or more metal-based particles, extremely strong plasmon resonance and extension of the plasmon resonance action range are expressed by the interaction between localized plasmons of the metal-based particles.

  When the metal-based particle aggregate [i] is applied to the optical element as an enhancement element, the number of metal-based particles contained in the metal-based particle aggregate [i] is, for example, in light of the general element area of the optical element, It can be 300 or more, and further 17500 or more.

The number density of metal particles in the metal particle aggregate [i] is preferably 7 particles / μm ² or more, and more preferably 15 particles / μm ² or more.

  Further, as described above, in the metal-based particle aggregate [i], the metal-based particles are insulated from each other, that is, nonconductive with respect to adjacent metal-based particles (non-conductive as a metal-based particle aggregate). Preferably).

(Metal-based particle aggregate [ii])
The metal-based particle aggregate [ii] is extremely advantageous in the following points.

  (I) In the absorption spectrum in the visible light region, the maximum wavelength of the plasmon peak on the longest wavelength side exists in a specific wavelength region. Specifically, when the metal-based particle aggregate [ii] has an absorption spectrum, the maximum wavelength of the plasmon peak is 30 to more than the maximum wavelength of the reference metal-based particle aggregate (X) described later. It shifts to the short wavelength side (blue shift) in the range of 500 nm (for example, in the range of 30 to 250 nm), and typically the maximum wavelength of the plasmon peak is in the range of 350 to 550 nm.

  Such a metal-based particle aggregate [ii] that can have a plasmon peak in blue or in the vicinity wavelength region thereof is extremely useful for enhancing light emission of a light-emitting element using a light-emitting material in blue or in the vicinity wavelength region, In a light-emitting device including such a metal-based particle aggregate [ii], even when a blue light-emitting material having a relatively low light emission efficiency is used, the light emission efficiency can be enhanced to a sufficient level. In addition, when applied to photoelectric conversion elements (solar cell elements, etc.), for example, the wavelength region that could not be used in the active layer itself can be effectively utilized by blue shifting the resonance wavelength, thereby improving the conversion efficiency. obtain.

  The blue shift has a structure in which the metal-based particle aggregate [ii] has a structure in which a specific number or more of large-sized metal-based particles having a specific shape are two-dimensionally spaced. This is thought to be due to the interaction between the local plasmons of the system particles.

  Here, when comparing the maximum wavelength of the peak on the longest wavelength side and the absorbance at the maximum wavelength between a certain metal-based particle assembly and the reference metal-based particle assembly (X), Using an “OPTIPHOT-88” manufactured by Nikon and a spectrophotometer (“MCPD-3000” manufactured by Otsuka Electronics Co., Ltd.), the absorption spectrum is measured with the measurement field of view narrowed.

  The reference metal-based particle aggregate (X) is obtained by replacing the metal-based particles A having the same average particle diameter, the same particle size, the same height as the average height, and the same material with the metal particle aggregates to be subjected to absorption spectrum measurement. An assembly of metal particles arranged such that the distances between the system particles are all within the range of 1 to 2 μm, and the absorption spectrum measurement using the above microscope can be performed in a state of being laminated on the glass substrate. It has a size.

  The absorption spectrum waveform of the reference metal-based particle aggregate (X) includes the particle size and height of the metal-based particle A, the dielectric function of the material of the metal-based particle A, and the dielectric function of the medium (for example, air) around the metal-based particle A. It is also possible to theoretically calculate by the 3D-FDTD method using the dielectric function of the substrate (for example, a glass substrate).

  Further, the metal-based particle aggregate [ii] has a structure in which a specific number or more of relatively large metal-based particles having a specific shape are arranged two-dimensionally apart from each other, (II) Extremely strong plasmon resonance can be exhibited (similar to the effect (1) of the metal-based particle aggregate [i]), and (III) the range of action of plasmon resonance (the range over which the plasmon enhances) is significantly extended. (Similar to the effect (2) of the metal-based particle aggregate [i]). The metal-based particle aggregate [ii] has an absorbance at the maximum wavelength of the plasmon peak on the longest wavelength side in the visible light region when the absorption spectrum is measured in a state where the metal particle aggregate [ii] is laminated on the glass substrate, Furthermore, it can be 0.7 or more, and even 0.9 or more.

  The specific configuration of the metal-based particle aggregate [ii] is the specific configuration of the metal-based particle aggregate [i] (the material of the metal-based particles, the average particle diameter, the average height, the aspect ratio, the average interparticle distance, the metal The number of the system particles, the non-conductivity of the metal-based particle aggregate, etc.) can be basically the same. Definitions of terms such as average particle diameter, average height, aspect ratio, and average interparticle distance are the same as those for the metal-based particle aggregate [i].

  The average particle diameter of the metal-based particles is in the range of 200 to 1600 nm, and in order to effectively obtain the effects (I) to (III), preferably 200 to 1200 nm, more preferably 250 to 500 nm, still more preferably Is in the range of 300-500 nm. By forming an aggregate in which a predetermined number (30) or more of such large metal particles are two-dimensionally arranged, it is possible to realize extremely strong plasmon resonance and a significant extension of the plasmon resonance operating range. Further, in order to develop the above feature [ii] (plasmon peak shift to the short wavelength side), the metal particles must have an average particle size of 200 nm or more, preferably 250 nm or more. . The average particle diameter of the metal-based particles is preferably selected appropriately depending on the type of optical element to which the metal-based particle aggregate is applied as an enhancement element and the type of material constituting the metal-based particles.

  In the metal-based particle aggregate [ii], the maximum wavelength of the plasmon peak on the longest wavelength side in the visible light region depends on the average particle diameter of the metal-based particles. That is, when the average particle diameter of the metal-based particles exceeds a certain value, the maximum wavelength of the plasmon peak shifts (blue shift) to the short wavelength side.

  The average height of the metal-based particles is in the range of 55 to 500 nm, and in order to effectively obtain the effects (I) to (III), preferably in the range of 55 to 300 nm, more preferably 70 to 150 nm. It is. The aspect ratio of the metal-based particles is in the range of 1 to 8, and, as in the case of the metal-based particle aggregate [i], it is appropriate depending on the type of optical element to which the metal-based particle aggregate is applied as an enhancement element. It is preferable to select.

  In the metal particle aggregate [ii], the metal particles are preferably arranged so that the average interparticle distance is in the range of 1 to 150 nm. More preferably, it is 1-100 nm, More preferably, it is 1-50 nm, Most preferably, it exists in the range of 1-20 nm. By arranging the metal-based particles densely as described above, the interaction between the local plasmons of the metal-based particles is effectively generated, and the effects (I) to (III) are easily expressed. Since the maximum wavelength of the plasmon peak depends on the average interparticle distance of the metal particles, the degree of blue shift of the plasmon peak on the longest wavelength side and the maximum wavelength of the plasmon peak are controlled by adjusting the average interparticle distance. Is possible. When the average interparticle distance is less than 1 nm, electron transfer based on the Dexter mechanism occurs between particles, which is disadvantageous in terms of deactivation of localized plasmons.

  The number of metal particles contained in the metal particle aggregate [ii] is 30 or more, and preferably 50 or more. By forming an aggregate including 30 or more metal-based particles, an interaction between localized plasmons of the metal-based particles is effectively generated, and the characteristics of [ii] and the effects of (I) to (III) are achieved. Expression is possible.

When applying the metal-based particle aggregate [ii] to the optical element as an enhancement element, in light of the general element area of the optical element, the number of metal-based particles included in the metal-based particle aggregate [ii] is, for example, It can be 300 or more, and further 17500 or more. The number density of metal particles in the metal particle aggregate [ii] is preferably 7 particles / μm ² or more, and more preferably 15 particles / μm ² or more.

(Metal-based particle aggregate [iii])
The metal-based particle aggregate [iii] is extremely advantageous in the following points.

  (A) The reference at the maximum wavelength of the peak on the longest wavelength side in the visible light region, which is a plasmon peak, can be regarded as an aggregate in which metal-based particles are simply aggregated without any interparticle interaction. Since it is larger than the metal-based particle aggregate (Y) and thus exhibits extremely strong plasmon resonance, when applied to a light-emitting element, a stronger emission enhancement effect is obtained compared to the case of using a conventional plasmon material. As a result, the luminous efficiency can be dramatically increased. Further, when applied to a photoelectric conversion element, this conversion efficiency can be dramatically increased. Such strong plasmon resonance is considered to be expressed by the interaction between localized plasmons of metal-based particles.

  As described above, from the magnitude of the absorbance value at the maximum wavelength of the plasmon peak, it is possible to roughly evaluate the intensity of the plasmon resonance of the plasmon material, but the metal-based particle aggregate [iii] When the absorption spectrum is measured in the state of being laminated on the glass substrate, the absorbance at the maximum wavelength of the plasmon peak on the longest wavelength side in the visible light region is 0.4 or more, further 0.7 or more, and even more preferably 0.8. It can be 9 or more.

  As described above, when comparing the maximum wavelength of the peak on the longest wavelength side and the absorbance at the maximum wavelength between a certain metal-based particle assembly and the reference metal-based particle assembly (Y), Using a microscope ("OPTIPHOT-88" manufactured by Nikon Corporation) and a spectrophotometer ("MCPD-3000" manufactured by Otsuka Electronics Co., Ltd.), the absorption spectrum is measured by narrowing the measurement field of view.

  The reference metal-based particle aggregate (Y) is obtained by replacing the metal-based particles B having the same average particle size, average particle size, height and same material as the average particle diameter of the metal-based particle aggregate that is the target of absorption spectrum measurement. An assembly of metal particles arranged such that the distances between the system particles are all within the range of 1 to 2 μm, and the absorption spectrum measurement using the above microscope can be performed in a state of being laminated on the glass substrate. It has a size.

  When comparing the absorbance at the maximum wavelength of the peak on the longest wavelength side between the metal-based particle aggregate to be subjected to the absorption spectrum measurement and the reference metal-based particle aggregate (Y), the following is described. Next, an absorption spectrum of the reference metal-based particle aggregate (Y) converted so as to have the same number of metal-based particles is obtained, and the absorbance at the maximum wavelength of the peak on the longest wavelength side in the absorption spectrum is used for comparison. . Specifically, the absorption spectrum of each of the metal-based particle assembly and the reference metal-based particle assembly (Y) is obtained, and the absorbance at the maximum wavelength of the peak on the longest wavelength side in each of the absorption spectra is expressed as the coverage ratio. The value divided by (the coverage of the substrate surface with the metal particles) is calculated and compared.

  Further, the metal particle aggregate [iii] has a structure in which a specific number or more of relatively large metal particles having a specific shape are arranged two-dimensionally apart from each other, (B) The action range of plasmon resonance (the range in which the enhancement effect by plasmons can be extended) can be significantly extended (similar to the effect (2) of the metal-based particle aggregate [i] above), and (c) the maximum wavelength of the plasmon peak Can exhibit a peculiar shift (similar to the effect (3) of the metal-based particle aggregate [i]).

  The metal-based particle aggregate [iii] (in the state of being laminated on the glass substrate) has the longest absorption spectrum in the visible light region measured by the absorptiometry according to the shape of the metal-based particles and the average interparticle distance. The plasmon peak on the wavelength side can exhibit a maximum wavelength in a wavelength region of 350 to 550 nm, for example. The metal-based particle aggregate [iii] is typically about 30 to 500 nm (for example 30 to 30 nm) as compared with the case where the metal-based particles are arranged with a sufficiently long inter-particle distance (for example, 1 μm). 250 nm) blue shift can occur.

  The specific configuration of the metal-based particle aggregate [iii] is the specific configuration of the metal-based particle aggregate [i] (the material of the metal-based particles, the average particle diameter, the average height, the aspect ratio, the average interparticle distance, the metal The number of the system particles, the non-conductivity of the metal-based particle aggregate, etc.) can be basically the same. Definitions of terms such as average particle diameter, average height, aspect ratio, and average interparticle distance are the same as those for the metal-based particle aggregate [i].

  The average particle diameter of the metal-based particles is in the range of 200 to 1600 nm, and the above-mentioned feature [iii] (the absorbance at the maximum wavelength of the plasmon peak on the longest wavelength side is that of the reference metal-based particle aggregate (Y)). In order to effectively obtain the effects (a) to (c) above, it is preferably in the range of 200 to 1200 nm, more preferably 250 to 500 nm, still more preferably 300 to 500 nm. . Thus, it is important to form relatively large metal particles, and by forming an aggregate in which a predetermined number (30) or more of large metal particles are two-dimensionally arranged, extremely strong plasmons are obtained. It is possible to realize a significant extension of the action range of resonance and further plasmon resonance and shift of the plasmon peak to the short wavelength side. The average particle diameter of the metal-based particles is preferably selected appropriately depending on the type of optical element to which the metal-based particle aggregate is applied as an enhancement element and the type of material constituting the metal-based particles.

  The average height of the metal-based particles is in the range of 55 to 500 nm, and in order to effectively obtain the characteristics of [iii] above, and further the effects (a) to (c) above, preferably 55 to 300 nm, More preferably, it exists in the range of 70-150 nm. The aspect ratio of the metal-based particles is in the range of 1 to 8, and, as in the case of the metal-based particle aggregate [i], it is appropriate depending on the type of optical element to which the metal-based particle aggregate is applied as an enhancement element. It is preferable to select.

  Since the characteristics of [iii] can be effectively obtained, the metal-based particles constituting the metal-based particle aggregate [iii] are as uniform in shape (average particle diameter, average height, aspect ratio) as possible. Preferably there is. That is, by making the shape of the metal-based particles uniform, the plasmon peak is sharpened, and accordingly, the absorbance of the plasmon peak on the longest wavelength side is higher than that of the reference metal-based particle aggregate (Y). It becomes easy. Reduction of variation in shape between metal-based particles is advantageous from the viewpoint of uniformity of plasmon resonance strength in the plane of the metal-based particle assembly. However, as described above, even if there is some variation in the particle size, it is not preferable that the distance between the large particles increases, and the interaction between the large particles is facilitated by filling the space between the small particles. It is preferable.

  In the metal particle aggregate [iii], the metal particles are preferably arranged so that the average interparticle distance is in the range of 1 to 150 nm. More preferably, it is 1-100 nm, More preferably, it is 1-50 nm, Most preferably, it exists in the range of 1-20 nm. By arranging the metal-based particles densely as described above, the interaction between the localized plasmons of the metal-based particles is effectively generated, and the characteristics of [iii] above, and further the effects (a) to (c) above. Can be effectively expressed. When the average interparticle distance is less than 1 nm, electron transfer based on the Dexter mechanism occurs between particles, which is disadvantageous in terms of deactivation of localized plasmons.

  The number of metal particles contained in the metal particle aggregate [iii] is 30 or more, and preferably 50 or more. By forming an aggregate containing 30 or more metal-based particles, an interaction between localized plasmons of the metal-based particles is effectively generated, and the characteristics of [iii] above, and further the above (a) to (c) The effect of can be expressed effectively.

When the metal-based particle aggregate [iii] is applied to the optical element as an enhancement element, in light of the general element area of the optical element, the number of metal-based particles included in the metal-based particle aggregate [iii] is, for example, It can be 300 or more, and further 17500 or more. The number density of the metal particles in the metal particle aggregate [iii] is preferably 7 particles / μm ² or more, and more preferably 15 particles / μm ² or more.

  As described above, the metal-based particle aggregate [iii] can be obtained by controlling the metal species and shape of the metal-based particles constituting the metal-based particle aggregate [iii] and the average distance between the metal-based particles.

  The metal-based particle aggregate suitable as an enhancement element of the optical element obtainable by the production method of the present invention more preferably has any two or more features of [i] to [iii], and more preferably It has all the features [i] to [iii].

  As described above, the production method of the present invention includes an insulating layer forming step after the metal-based particle assembly forming step (B), and covers the surface of each metal-based particle on the thin film of the metal-based particle assembly. May be formed. Such an insulating layer is not only preferable for ensuring the non-conductivity (non-conductivity between metal-based particles) of the metal-based particle assembly described above, but also when the metal-based particle assembly is applied to an optical element. Also preferred. That is, in an optical element such as an electric energy-driven light-emitting element or photoelectric conversion element, a current flows in each layer constituting the element, but if the current flows in the metal-based particle aggregate, the enhancement effect by plasmon resonance is sufficient. May not be obtained. By providing an insulating layer that caps the metal-based particle aggregate, electrical insulation between the metal-based particle aggregate and the constituent layer of the optical element adjacent thereto can be achieved even when applied to an optical element. Therefore, current can be prevented from being injected into the metal-based particles constituting the metal-based particle aggregate.

The material constituting the insulating layer is not particularly limited as long as it has good insulating properties. For example, in addition to spin-on glass (SOG; for example, containing an organic siloxane material), SiO ₂ or Si ₃ N ₄ Etc. can be used. The thickness of the insulating layer is not particularly limited as long as desired insulating properties are ensured, but an active layer when applied to an optical element as described later (for example, a light emitting layer of a light emitting element or a light absorbing layer of a photoelectric conversion element). Since the distance between the metal particle aggregate and the metal-based particle aggregate is preferably as short as possible, it is preferable that the distance is as small as possible within a range in which desired insulation is ensured.

  The metal-based particle aggregate obtained by the production method of the present invention can be incorporated into various optical elements in a state of being integrated with a substrate used for producing the metal-based particle aggregate.

  As described above, the metal-based particle aggregates [i] to [iii] that can be obtained by the production method of the present invention exhibit extremely strong plasmon resonance, and further, the action range of plasmon resonance (range of enhancement effect by plasmon) For example, the entire active layer having a thickness of 10 nm or more, further 20 nm or more, and even more can be enhanced. In addition, the active layer disposed at a position separated by, for example, 10 nm, further several tens of nm (for example, 20 nm), or even several hundred nm or more can be enhanced extremely effectively.

  In addition, since the enhancement effect by plasmon tends to become smaller as the distance between the active layer and the metal-based particle aggregate increases, the smaller the distance, the better. The distance between the active layer and the metal-based particle aggregate is preferably 100 nm or less, more preferably 20 nm or less, and further preferably 10 nm or less.

  The maximum wavelength of the emission wavelength (for example, in the case of a light emitting device) or the absorption wavelength (for example in the case of a photoelectric conversion device) exhibited by the active layer is preferably equal to or close to the maximum wavelength of the plasmon peak of the metal-based particle aggregate. Thereby, the enhancement effect by plasmon resonance can be enhanced more effectively. The maximum wavelength of the plasmon peak of the metal particle aggregate can be controlled by adjusting the metal species, average particle diameter, average height, aspect ratio and / or average particle distance of the metal particles constituting the metal particle aggregate.

  The light emitting layer is, for example, 1) composed of a monomolecular film in which dye molecules are arranged in a plane, 2) composed of a matrix doped with dye molecules, 3) composed of a light emitting low molecule, 4) It can be made of a light-emitting polymer.

  The light emitting layer of 1) can be obtained by a method of removing the solvent after spin-coating the dye molecule-containing liquid. Specific examples of the dye molecule include rhodamine 101, rhodamine 110, rhodamine 560, rhodamine 6G, rhodamine B, rhodamine 640, rhodamine 700 and other rhodamine dyes sold by Exciton, coumarin 503 sold by Exciton, etc. Including coumarin pigments.

  The light emitting layer of 2) can be obtained by a method of spin-coating a liquid containing dye molecules and a matrix material and then removing the solvent. As the matrix material, a transparent polymer such as polyvinyl alcohol or polymethyl methacrylate can be used. Specific examples of the dye molecule can be the same as those in the light emitting layer of 1).

The light emitting layer 3) can be obtained by a dry or wet film forming method including a spin coating method and a vapor deposition method. Specific examples of the light-emitting small molecule include tris (8-quinolinolato) aluminum complex [tris (8-hydroxyquinoline) aluminum complex; Alq ₃ ], bis (benzoquinolinolato) beryllium complex [BeBq] and the like.

  The light emitting layer of 4) can be obtained by a wet film forming method using a light emitting polymer-containing liquid such as a spin coat method. Specific examples of the light-emitting polymer include π-conjugated polymers such as F8BT [poly (9,9-dioctylfluorene-alt-benzothiadiazole)], poly (p-phenylenevinylene), and polyalkylthiophene.

  The metal-based particle aggregates [i] to [iii] have been mainly described as the metal-based particle aggregates that can be obtained by the production method of the present invention. However, the metal-based particle aggregates that can be obtained by the production method of the present invention. A particle aggregate is one in which any one or more of the number of metal particles, shape of metal particles (average particle diameter, average height, aspect ratio), and average interparticle distance are not within the above range. It may be. Such metal-based particle aggregates may not be as advantageous as the metal-based particle aggregates [i] to [iii] in terms of the enhancement effect by plasmons, but they are still equivalent to conventional plasmon materials Or, since it can exhibit a further enhancement effect, it can be applied to an enhancement element of an optical element.

  Moreover, the metal-based particle assembly and the metal-based particle assembly laminated substrate of the present invention can be used for analysis applications and color material applications. The analytical application includes application to surface enhanced Raman spectroscopy using surface enhanced Raman scattering. Examples of the color material use include use as a color imparting material for various articles (automobiles, ceramics, etc.). In addition, when used as a color filter, color rendering that is difficult to achieve with pigments and pigments can be achieved. Examples of the color filter include a filter that transmits only light having a specific wavelength or blocks light having a specific wavelength.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these Examples. In addition, the average thickness of the silver film before the heat treatment is such that a peeling line (scratch) reaching the substrate is provided on the outer surface of the metal film with tweezers, and the cross section of the metal film at the peeling line and the interface between the metal film and the substrate Is obtained as an average value of 10 points when the distance from the metal film side surface of the substrate to the outer surface of the metal film is randomly determined based on the AFM image. did.

<Example 1>
(1) Preparation of metal-based particle aggregate Silver nanoparticle aqueous dispersion (manufactured by Mitsubishi Paper Industries, Ltd., silver nanoparticle concentration: 25% by weight, average particle diameter of silver nanoparticles: 15 nm) with pure water, silver nanoparticle concentration Was diluted to 2% by weight. Next, after adding 1% by volume of the surfactant to the diluted silver nanoparticle aqueous dispersion and stirring well, 80% by volume of acetone was added to the obtained silver nanoparticle aqueous dispersion. The mixture was sufficiently stirred at room temperature to prepare a coating solution.

  Next, after spin-coating the said coating liquid at 1000 rpm on the 1-mm-thick soda glass board | substrate which wiped the surface with acetone, it was left to stand in air | atmosphere for 1 minute as it was. The average thickness of the obtained silver film was 21.6 nm. Thereafter, the soda glass substrate on which the silver film was formed was placed in an electric furnace at 550 ° C., and was subjected to heat treatment (firing) for 40 seconds in an air atmosphere to obtain a metal-based particle assembly 1-1.

  Next, the coating solution was spin-coated again at 1000 rpm on the obtained metal-based particle assembly 1-1, and then left as it was in the atmosphere for 1 minute. Thereafter, the soda glass substrate on which the silver film and the metal-based particle aggregate 1-1 are formed is placed in an electric furnace at 550 ° C. and subjected to heat treatment (firing) for 40 seconds in an air atmosphere. 2 was obtained.

  Next, the coating solution was spin-coated again at 1000 rpm on the obtained metal-based particle aggregate 1-2, and then left as it was in the atmosphere for 1 minute. Thereafter, the soda glass substrate on which the silver film and the metal-based particle aggregate 1-2 are formed is placed in an electric furnace at 550 ° C. and subjected to heat treatment (firing) for 40 seconds in an air atmosphere. 3 was obtained.

  FIG. 2 is an AFM image showing the metal-based particle aggregate 1-1. “VN-8010” manufactured by Keyence Corporation was used for AFM image shooting (the same applies hereinafter). The image size of this AFM image is 5 μm × 5 μm (the same applies to the following AFM images). From this AFM image, the average height of the silver particles constituting the metal-based particle aggregate 1-1 was determined to be 62.4 nm.

FIG. 3 is an SEM image when the metal-based particle aggregate 1-2 is viewed from directly above. FIG. 3A is an enlarged image on a 10000 times scale, and FIG. 3B is an enlarged image on a 50000 times scale. FIG. 4 is an AFM image showing the metal-based particle aggregate 1-2. From the SEM image shown in FIG. 3, the average particle size of the silver particles constituting the metal-based particle assembly 1-2 was determined to be 293 nm, and the average interparticle distance was determined to be 107.8 nm. From the AFM image shown in FIG. 4, the average height was determined to be 93.0 nm. From these, the aspect ratio (average particle diameter / average height) of the silver particles is calculated to be 3.15, and it can be seen from the acquired image that the silver particles have a flat shape. Furthermore, it can be seen from the SEM image that the metal-based particle aggregate 1-2 has about 3.13 × 10 ¹⁰ (about 12.5 particles / μm ² ) silver particles.

  FIG. 5 is an AFM image showing the metal-based particle aggregate 1-3. From this AFM image, the average height of the silver particles constituting the metal-based particle assembly 1-3 was determined to be 140.7 nm.

  Moreover, about the metallic particle aggregates 1-1 to 1-3, when a tester [multimeter (“E2378A” manufactured by Hewlett-Packard Co., Ltd.)] is connected to the surface thereof to confirm the conductivity, the metal particle aggregates 1-1 to 1-3 have no conductivity. Was confirmed.

(2) Measurement of Absorption Spectrum of Metal Particle Aggregation 1-2 FIG. 6 is an absorption spectrum measured by an absorptiometry of the metal particle aggregate 1-2 (in a state of being laminated on the substrate). Non-patent literature (K. Lance Kelly, et al., "The Optical Properties of Metal Nanoparticles: The Influence of Size, Shape, and Dielectric Environment", The Journal of Physical Chemistry B, 2003, 107, 668) As shown in the figure, when the flat silver particles are not aggregates but alone, they have a plasmon peak around 550 nm when the average particle size is 200 nm and around 650 nm when the average particle size is 300 nm. It is common.

  On the other hand, the metal-based particle aggregate 1-2 has the longest wavelength in the visible light region, as shown in FIG. 6, even though the average particle diameter of the silver particles constituting the metal-based particle aggregate 1-2 is about 300 nm (293 nm). It can be seen that the maximum wavelength of the plasmon peak on the side is 488 nm, shifted to the short wavelength side. This phenomenon is considered to be because a predetermined number or more of silver particles have the above-mentioned predetermined shape, and the silver particles are preferably arranged very densely. It can also be seen that the absorbance at the maximum wavelength of the plasmon peak on the longest wavelength side in the visible light region is about 0.45, indicating strong plasmon resonance.

The absorption spectrum shown in FIG. 6 is the back side of the glass substrate on which the metal-based particle aggregates are laminated (the side opposite to the metal-based particle aggregates), and is ultraviolet to visible from the direction perpendicular to the substrate surface. Irradiated with light in the light region and transmitted to the metallic particle aggregate side in all directions, the transmitted light intensity I is the same thickness and material as the substrate, and the metallic particle aggregate is not laminated. It is obtained by irradiating the same incident light from the direction perpendicular to the surface of the substrate and measuring the intensity I ₀ of transmitted light in all directions transmitted from the opposite side of the incident surface using an integrating sphere spectrophotometer. It is what was done. The absorbance on the vertical axis is the following formula:
Absorbance = −log ₁₀ (I / I ₀ )
It is represented by

(3) Preparation of reference metal-based particle aggregate and measurement of absorption spectrum thereof A substrate on which the reference metal-based particle aggregate was laminated was manufactured according to the method shown in FIG. First, a resist (ZEP520A manufactured by Nippon Zeon Co., Ltd.) was spin-coated on approximately the entire surface of a substrate 100 made of soda glass having a length of 5 cm and a width of 5 cm (FIG. 7A). The thickness of the resist 400 was about 120 nm. Next, a circular opening 401 was formed in the resist 400 by electron beam lithography (FIG. 7B). The diameter of the circular opening 401 was about 350 nm. The distance between the centers of the adjacent circular openings 401 was set to about 1500 nm.

  Next, a silver film 410 was deposited on the resist 400 having the circular opening 401 by a vacuum deposition method (FIG. 7C). The film thickness of the silver film 410 was about 100 nm. Finally, the substrate having the silver film 410 is dipped in NMP (N-methyl-2-pyrrolidone manufactured by Tokyo Chemical Industry Co., Ltd.) and left at room temperature in an ultrasonic device for 1 minute to form a film on the resist 400 and the resist 400. The formed silver film 410 was peeled off, and only the silver film 410 (silver particles) in the circular opening 401 remained on the substrate 100 to obtain a laminated reference metal particle aggregate (FIG. 7D).

  FIG. 8 is an SEM image when the obtained reference metal-based particle aggregate is viewed from directly above. FIG. 8A is an enlarged image on a 20000 times scale, and FIG. 8B is an enlarged image on a 50000 times scale. From the SEM image shown in FIG. 8, the average particle diameter based on the above definition of the silver particles constituting the reference metal-based particle aggregate was determined to be 333 nm, and the average interparticle distance was 1264 nm. The average height was determined to be 105.9 nm from the separately acquired AFM image. Further, from the SEM image, it was found that the reference metal-based particle aggregate had about 62500 silver particles.

(4) Absorption spectrum measurement comparison between the metal-based particle assembly 1-2 and the reference metal-based particle assembly According to the measurement method using the above-described microscope objective lens (100 times), the metal-based particle assembly 1-2 ( The absorption spectrum was measured in the state of being laminated on the substrate. Specifically, referring to FIG. 9, the substrate 501 side (the side opposite to metal-based particle assembly 502) of metal-based particle assembly laminated substrate 500 is a visible light region from a direction perpendicular to the substrate surface. Of incident light. Then, the transmitted light that has passed through the metal-based particle aggregate 502 side and reached the 100 × objective lens 600 is collected by the objective lens 600, and this condensed light is detected by the spectrophotometer 700 to obtain an absorption spectrum. Obtained. The spectrophotometer 700 was an ultraviolet-visible spectrophotometer “MCPD-3000” manufactured by Otsuka Electronics Co., Ltd., and the objective lens 600 was a “BD Plan 100 / 0.80 ELWD” manufactured by Nikon.

  As a result, the maximum wavelength of the plasmon peak on the longest wavelength side in the visible light region was 516 nm. On the other hand, when the absorption spectrum of the reference metal-based particle aggregate was measured by the same measurement method using a microscope objective lens, the maximum wavelength of the peak on the longest wavelength side in the visible light region was 654 nm. In the metal-based particle assembly 1-2, the peak maximum wavelength on the longest wavelength side in the visible light region is blue-shifted by about 170 nm compared to the reference metal-based particle assembly.

  According to the measurement method using the objective lens (100 times) of the microscope, the metal-based particle aggregate 1-2 has an absorbance at a maximum wavelength of a peak on the longest wavelength side in the visible light region of 0.563. The reference metal-based particle aggregate was 0.033. To compare the absorbance at the maximum wavelength of the peak on the longest wavelength side between the metal-based particle assembly 1-2 and the reference metal-based particle assembly so as to make a comparison with the same number of metal-based particles The absorbance / coverage was calculated by dividing the absorbance obtained from the absorption spectrum by the coverage of the substrate surface with metal particles, which is a parameter corresponding to the number of metal particles. The absorbance / coverage of the metal-based particle assembly 1-2 was 1.04 (coverage 54.2%), and the absorbance / coverage of the reference metal-based particle assembly was 0.84 (coverage 3). .9%).

<Examples 2 to 4>
(1) Preparation of metal-based particle aggregate Silver nanoparticle aqueous dispersion (manufactured by Mitsubishi Paper Industries, Ltd., silver nanoparticle concentration: 25% by weight, average particle diameter of silver nanoparticles: 15 nm) with pure water, silver nanoparticle concentration Was diluted to 2% by weight. Next, after adding 1% by volume of the surfactant to the diluted silver nanoparticle aqueous dispersion and stirring well, 80% by volume of acetone was added to the obtained silver nanoparticle aqueous dispersion. The mixture was sufficiently stirred at room temperature to prepare a coating solution.

  Next, the coating solution was spin-coated at 1500 rpm on a 1 mm thick soda glass substrate whose surface was wiped with acetone, and then left in the atmosphere for 1 minute. The average thickness of the obtained silver film was 18.0 nm. Thereafter, the soda glass substrate on which the silver film was formed was placed in an electric furnace at 550 ° C., and was subjected to heat treatment (firing) for 8 minutes in an air atmosphere to obtain a metal-based particle aggregate 2 (Example 2).

  Further, metal-based particles were prepared in the same manner as in Example 2 except that the silver nanoparticle aqueous dispersion manufactured by Mitsubishi Paper Industries was diluted with pure water so that the silver nanoparticle concentrations were 4 wt% and 6 wt%, respectively. Aggregates 3 and 4 were obtained (Examples 3 and 4 respectively). The average thickness of the silver film before heat treatment in Example 3 was 24.3 nm, and in Example 4 it was 28.2 nm.

  FIG. 10 is an AFM image showing the metal-based particle assembly 2. From this AFM image, the average height of the silver particles constituting the metal-based particle assembly 2 was determined to be 8.5 nm.

FIG. 11 is an SEM image when the metal-based particle assembly 4 is viewed from directly above, and is an enlarged image on a 10000 times scale. FIG. 12 is an AFM image showing the metal-based particle assembly 4. From the SEM image shown in FIG. 11, the average particle diameter of the silver particles constituting the metal-based particle assembly 4 was determined to be 278 nm, and the average interparticle distance was determined to be 195.5 nm. From the AFM image shown in FIG. 12, the average height was determined to be 99.5 nm. From these, the aspect ratio (average particle diameter / average height) of the silver particles is calculated to be 2.79, and it can be seen from the acquired image that the silver particles have a flat shape. Furthermore, it can be seen from the SEM image that the metal-based particle aggregate 4 has about 2.18 × 10 ¹⁰ (about 8.72 particles / μm ² ) silver particles.

  Moreover, about the metal-type particle aggregates 2-4, when the tester [Multimeter ("E2378A" made by Hewlett-Packard Co., Ltd.)] was connected to the surface and the conductivity was confirmed, it was confirmed that there was no conductivity. .

(2) Absorption spectrum measurement of metal-based particle assemblies 2 to 4 FIG. 13 is an absorption spectrum measured by absorptiometry of metal-based particle assemblies 2 to 4 (in a state of being stacked on a substrate). The method for measuring the absorption spectrum is the same as in FIG. It can be seen that all of the metal-based particle assemblies 2 to 4 have strong plasmon resonance because the absorbance at the maximum wavelength of the plasmon peak on the longest wavelength side in the visible light region is about 0.4 or more. Therefore, these metal-based particle aggregates can be applied to plasmon materials, for example, the aforementioned analytical use and color material use. Furthermore, for example, it can be used as an enhancement element for improving the light emission efficiency of the light emitting element and the conversion efficiency of the photoelectric conversion element.

  Moreover, it can be seen from the absorption spectrum of FIG. 13 that the maximum wavelength of the plasmon peak can be controlled over a wide range by adjusting the silver nanoparticle concentration in the coating solution, and thus the average thickness of the silver film before the heat treatment. The ability to control the maximum wavelength of the plasmon peak to a desired wavelength is useful, for example, in that a color tone adapted to a desired application can be obtained in a color material application, and in an analytical application, wavelength adjustment can be performed according to an analysis target, This is useful in that a highly sensitive analysis can be realized.

<Example 5-1>
In the same manner as in Example 1, a metal particle aggregate 1-2 was formed on a 0.5 mm thick soda glass substrate. Immediately thereafter, an SOG (spin-on-glass) solution was spin-coated on the metal-based particle aggregate 1-2, and an insulating layer having an average thickness of 10 nm was laminated. As the SOG solution, an organic SOG material “OCD T-7 5500T” manufactured by Tokyo Ohka Kogyo Co., Ltd. diluted with ethanol was used. The “average thickness” as used herein means that spin coating was directly performed on a soda glass substrate under the same conditions as when forming on a metal-based particle aggregate (same coating solution with the same composition in the same area). It is the average value of the thickness at arbitrary 5 points.

Next, an Alq ₃ light emitting layer solution was spin-coated on the insulating layer to form an Alq ₃ light emitting layer having an average thickness of 30 nm to obtain a photoexcited light emitting device. The solution for the Alq ₃ light-emitting layer was prepared by dissolving Alq ₃ (Sigma-Aldrich Tris- (8-hydroxyquinoline) aluminum) in chloroform so that the concentration was 0.5 wt%.

<Example 5-2>
A light emitting device was obtained in the same manner as in Example 5-1, except that the average thickness of the insulating layer was 30 nm.

<Example 5-3>
A light emitting device was obtained in the same manner as in Example 5-1, except that the average thickness of the insulating layer was 80 nm.

<Example 5-4>
A light emitting device was obtained in the same manner as in Example 5-1, except that the average thickness of the insulating layer was 150 nm.

  For each of the photoexcited light emitting devices of Examples 5-1, 5-2, 5-3, and 5-4, the degree of light emission enhancement was evaluated as follows. Referring to FIG. 14 (a) showing a measurement system of the emission spectrum of the photoexcited light emitting device and FIG. 14 (b) which is a schematic sectional view of the photoexcited light emitting device, the light emitting layer 2 is formed on the light emitting layer 2 side of the photoexcited light emitting device 1. The photoexcited light-emitting element 1 was caused to emit light by irradiating the excitation light 3 from a direction perpendicular to the surface of the substrate. As the excitation light source 4, a UV-LED (South Walker UV-LED 375-nano, excitation light wavelength: 375 nm) was used, and the light emitted from the excitation light source 4 was condensed by the lens 5 to be excitation light 3, which was irradiated. . A wavelength cut filter 8 (sigma optical machine) that collects the light emission 6 from the optical excitation light emitting element 1 emitted in the direction of 40 ° with respect to the optical axis of the excitation light 3 by the lens 7 and cuts the light having the wavelength of the excitation light. Through SCF-50S-44Y (manufactured by Co., Ltd.), the spectrophotometer 9 (MCPD-3000 manufactured by Otsuka Electronics Co., Ltd.) was used for detection. FIG. 14B is a schematic cross-sectional view showing the photoexcited light-emitting element 1 including a metal particle aggregate 200, an insulating layer 300, and a light emitting layer 2 in this order on a substrate 100 made of soda glass.

  The integrated value in the emission wavelength region was determined for the detected emission spectrum. The integrated value calculated | required from the emission spectrum measured about the optical excitation light emitting element of Example 5-1, 5-2, 5-3, 5-4 was used as the reference | standard reference light excitation light emitting element (a metal particle aggregate and an insulating layer). The light-excited light-emitting elements are the same as those in Examples 5-1 to 5-4 except that they are not included.) The value obtained by dividing the integrated value obtained from the measured emission spectrum is referred to as “emission enhancement magnification”. The obtained graph is shown in FIG.

<Example 6>
A silver nanoparticle aqueous dispersion (manufactured by Mitsubishi Paper Industries, Ltd., silver nanoparticle concentration: 25% by weight, silver nanoparticle average particle size: 15 nm) was diluted with pure water so that the silver nanoparticle concentration was 2% by weight. . Next, after adding 1% by volume of the surfactant to the diluted silver nanoparticle aqueous dispersion and stirring well, 80% by volume of acetone was added to the obtained silver nanoparticle aqueous dispersion. The mixture was sufficiently stirred at room temperature to prepare a coating solution. The silver nanoparticle density | concentration in this coating liquid is 1.2 weight%.

  Next, the coating solution was spin-coated at 1500 rpm on a 1 mm thick soda glass substrate whose surface was wiped with acetone, and then left in the atmosphere for 1 minute. The average thickness of the obtained silver film was 18.0 nm. Thereafter, the soda glass substrate on which the silver film was formed was placed in an electric furnace at 285 ° C., and was subjected to heat treatment (firing) for 5 minutes in an air atmosphere to obtain a metal-based particle aggregate 6.

<Example 7>
A silver deposition film was formed on a 1 mm thick soda glass substrate by vacuum deposition at a pressure of 2 × 10 ⁻³ Pa. The average thickness of the obtained silver vapor deposition film was 15.0 nm. Thereafter, the soda glass substrate on which the silver deposited film was formed was placed in an electric furnace at 350 ° C., and was subjected to heat treatment (firing) for 5 minutes in an air atmosphere to obtain a metal-based particle aggregate 7.

  16 and 17 are AFM images showing the metal-based particle aggregates 6 and 7 obtained in Examples 6 and 7, respectively. FIG. 18 is an absorption spectrum measured by the absorptiometry of the metal-based particle aggregates 6 and 7 (in a state of being stacked on the substrate). The method for measuring the absorption spectrum is the same as in FIG. As shown in FIG. 18, both of the metal-based particle assemblies 6 and 7 have an absorbance at the maximum wavelength of the plasmon peak on the longest wavelength side in the visible light region of about 0.6 or more, and exhibit strong plasmon resonance. You can see that Therefore, these metal-based particle aggregates can be used as a plasmon material, for example, an enhancement element for improving the light emission efficiency of the light emitting element and the conversion efficiency of the photoelectric conversion element. In addition, when the average thickness of the metal film is about 30 nm or less, a metal particle aggregate exhibiting a strong plasmon peak (showing a high plasmon resonance effect) is obtained even by heat treatment in a relatively low temperature region. It turns out that it is possible.

<Comparative Examples 1-2>
A silver deposition film was formed on a 1 mm thick soda glass substrate by vacuum deposition at a pressure of 2 × 10 ⁻³ Pa. The average thickness of the obtained silver vapor deposition film was 56.0 nm. Thereafter, the soda glass substrate on which the silver deposited film was formed was placed in an electric furnace at 300 ° C., and was subjected to heat treatment (firing) for 5 minutes in an air atmosphere to obtain a silver film H1 (Comparative Example 1).

  Further, a silver film H2 was obtained in the same manner as in Comparative Example 1 except that the deposition conditions were adjusted and the average thickness of the silver deposited film was 71.0 nm (Comparative Example 2).

  19 to 20 are AFM images showing the silver films H1 and H2 obtained in Comparative Examples 1 and 2, respectively. FIG. 21 is an absorption spectrum measured by an absorptiometry of the silver films H1 and H2 (in a state of being stacked on the substrate). The method for measuring the absorption spectrum is the same as in FIG. As shown in FIGS. 19 and 20, it was found that when the average thickness of the metal-based film before the heat treatment exceeds 50 nm, at least partially, the shape is not changed into the metal-based particle aggregate.

<Example 8 and Comparative Example 3>
A silver deposition film was formed on a 1 mm thick soda glass substrate by vacuum deposition at a pressure of 2 × 10 ⁻³ Pa. The average thickness of the obtained silver vapor deposition film was 39.0 nm. Thereafter, the soda glass substrate on which the silver deposited film was formed was placed in an electric furnace at 500 ° C., and was subjected to heat treatment (firing) for 5 minutes in an air atmosphere to obtain a metal-based particle aggregate 8 (Example 8). Further, a silver film H3 was obtained in the same manner as in Example 8 except that the deposition conditions were adjusted so that the average thickness of the silver deposited film was 56.0 nm (Comparative Example 3).

  22 to 23 are AFM images showing the metal-based particle aggregate 8 and the silver film H3 obtained in Example 8 and Comparative Example 3, respectively. FIG. 24 is an absorption spectrum of the metal-based particle aggregate 8 and the silver film H3 (in a state of being laminated on the substrate) measured by an absorptiometry. The method for measuring the absorption spectrum is the same as in FIG. As shown in FIG. 23, when the average thickness of the metal-based film before the heat treatment exceeds 50 nm, even if the heat treatment in the high-temperature region, the shape is not changed at least partially into the metal-based particle aggregate. I understood. Further, from the AFM image of FIG. 22 and the absorption spectrum of FIG. 24, when the average thickness of the metal-based film before heat treatment exceeds 30 nm but is 50 nm or less, strong plasmon resonance is caused by heat treatment in a high temperature region. It turned out that the metal type particle | grain aggregate which shows an effect is obtained.

  DESCRIPTION OF SYMBOLS 1 Photoexcitation light emitting element, 2 Light emitting layer, 3 Excitation light, 5,7 lens, 4 Excitation light source, 6 Light emission from photoexcitation light emitting element, 8 Wavelength cut filter, 9 Spectrometer, 100 Substrate, 200 Metal particle aggregate, 201 metal-based particles, 250 metal-based film, 255 surface region of pyrolyzed metal-based film, 300 insulating layer, 400 resist, 401 circular opening, 410 silver film, 500 metal-based particle assembly laminated substrate, 501 substrate, 502 metal System particle assembly, 600 objective lens, 700 spectrophotometer.

Claims (8)

A metal-based film forming step of forming a metal-based film having an average thickness of 50 nm or less on a substrate;
A metal-based particle assembly forming step of changing the shape of the metal-based film into a metal-based particle assembly in which a plurality of metal-based particles are two-dimensionally arranged apart from each other by heat treatment in an oxidizing atmosphere ; Including
The metal-based film forming step includes a step of forming the metal-based film on the substrate by a vapor deposition method, a sputtering method, or a plating method,
The method for producing a metal-based particle assembly, wherein the metal-based material constituting the metal-based film is a noble metal, aluminum, tantalum, or an alloy containing any of these.   The method for producing a metal-based particle assembly according to claim 1, wherein the temperature of the heat treatment is 280 ° C or higher.   The method for producing a metal-based particle assembly according to claim 1 or 2, wherein a series of steps including the metal-based film forming step and the subsequent metal-based particle assembly forming step are repeated twice or more. The metal particle aggregate includes 30 or more metal particles.
The metal-based particles have an average particle diameter in the range of 200 to 1600 nm, an average height in the range of 55 to 500 nm, and an aspect ratio defined by a ratio of the average particle diameter to the average height of 1 to 8 The metal-based particle assembly according to any one of claims 1 to 3, wherein the metal-based particle assembly is disposed so that an average distance between the adjacent metal-based particles is within a range of 1 to 150 nm. Production method. The metal particle aggregate includes 30 or more metal particles.
The metal-based particles have an average particle diameter in the range of 200 to 1600 nm, an average height in the range of 55 to 500 nm, and an aspect ratio defined by a ratio of the average particle diameter to the average height of 1 to 8 In the range of
In the absorption spectrum in the visible light region, the metal-based particle aggregate is a metal particle composed of the same particle size, the same height as the average height, and the same material as the average particle diameter. 2. The peak maximum wavelength on the longest wavelength side is shifted to the short wavelength side in the range of 30 to 500 nm as compared with the reference metal-based particle aggregate arranged to be in the range of 1 to 2 μm. The manufacturing method of the metal type particle aggregate in any one of -3. The metal particle aggregate includes 30 or more metal particles.
The metal-based particles have an average particle diameter in the range of 200 to 1600 nm, an average height in the range of 55 to 500 nm, and an aspect ratio defined by a ratio of the average particle diameter to the average height of 1 to 8 In the range of
In the absorption spectrum in the visible light region, the metal-based particle aggregate is a metal particle composed of the same particle size, the same height as the average height, and the same material as the average particle diameter. The absorbance at the maximum wavelength of the peak on the longest wavelength side is higher in comparison with the same number of metal-based particles than the reference metal-based particle aggregate disposed so as to fall within the range of 1 to 2 µm. A method for producing a metal-based particle assembly according to any one of the above.   The method for producing a metal-based particle assembly according to any one of claims 1 to 6, wherein the metal-based particles are made of a noble metal.   The method for producing a metal-based particle assembly according to claim 7, wherein the metal-based particles are made of silver.